When hydrogen gas is produced during the catalytic reformation of petroleum products, the gas is usually contaminated with about 2-5 ppm HCl. This chloride contamination results from chlorides that are injected into the system to regenerate the reforming catalyst. Hydrogen gas formed in the process leaches away chlorides from the catalyst so that the gas is eventually contaminated with HCl.
The hydrogen chloride may corrode metal components of downstream systems or result in formation of ammonium chloride. The salts formed may be deposited in openings of fuel system burners or compressor valves, thereby necessitating expensive repairs. Because of the corrosivity of HCl in downstream processing, there is a need to remove virtually all of it at least below 1 ppm levels.
In the prior art, alumina and some forms of molecular sieves have been used as adsorbents for hydrogen chloride. However, these prior art adsorbents each suffer from one or more serious disadvantages making them less than entirely suitable for their intended purpose.
Activated alumina is known to be an inexpensive adsorbent that is effective for removing high concentrations of hydrogen chloride from other gases. However, alumina is much less effective at low chloride concentrations (i.e. less than about 100 ppm) than at higher concentrations.
Various molecular sieves other than Y zeolite have been used in the prior art as adsorbents for small concentrations of HCl. However, these adsorbents are expensive and they are chemically degraded by HCl. Pure Y zeolites are particularly unsuitable as HCl adsorbents because they are so readily attacked.
The following are some prior patents disclosing adsorbents based upon combinations of alumina and molecular sieves: Figert U.S. Pat. No. 3,025,233; Chi et al U.S. Pat. No. 3,899,310; Michel U.S. Pat. No. 3,917,544; Podschus British No. 1,491,563. None of these patents discloses or suggests the composite adsorbent comprising alumina and Y zeolite that is claimed herein.
It is a principal objective of the present invention to provide a material that is an effective adsorbent for low concentrations of gaseous HCl while being chemically stable to HCl.
A related objective of the invention is to provide an HCl adsorbent requiring a shortened adsorber bed length to reduce HCl concentrations compared with prior art adsorbents.
Another objective of the invention is to provide a novel method for producing the composite adsorbent.
A further objective of the invention is to provide a method for removing HCl from a gas, using the composite adsorbent of the invention.
Additional objectives and advantages will become apparent to persons skilled in the art from the following specification and claims.